Communications between an ultrasonic transducer mounted or positioned on a movable stylus (such as a movable pen) and other remotely located transducers (for example, transducers fixed at remote positions from the stylus) make it possible to determine the position of the pen and ultimately to reproduce information associated with stylus movement. The digital information associated with the stylus position might be used for drawings, maps, or pictorial illustrations, as well as for e-mail, sending of facsimiles, document creations, document and file creation reproduction (in combination with a word processor), or input devices for computer games, for example.
It is known that a piezoelectric film (e.g. PVDF film) wrapped around a cylindrical surface may be configured as an ultrasonic acoustic transducer. In the case where the transducer in U.S. Pat. No. 6,239,535 entitled “Omni-directional Ultrasound Transducer Apparatus” issued May 29, 2001 having a controlled frequency response operates as a transmitter, an acoustic wave is excited by an applied voltage and radiated in a radial direction. In the case of a receiver, radial waves incident onto the ultrasonic device are received and converted to voltage signals. The basic principle of operation of such transducers is that the film length in the molecular chain direction (i.e. machined direction) varies by applied voltage (or length variation by applied force induces voltage). The film in the machined direction is curved to form a cylinder so that the radius varies by an applied voltage to excite an acoustic wave. In the case of a receiver, an incoming acoustic pressure induces a change of radius and length in the arcuated direction to generate a voltage signal. Such a device is disclosed in commonly assigned U.S. Pat. No. 6,239,535 issued to Toda, et al. and incorporated herein by reference. In the case of a transmitter, an AC signal applied to the film electrodes causes a corresponding acoustic wave to be emitted from the transducer.
The main acoustic beam direction of the above mentioned device is perpendicular to the axis of the cylinder on which the piezoelectric film is wrapped. In the case of an ultrasonic pen or stylus, the cylindrical ultrasonic transducer is mounted or positioned on a movable stylus such as a movable pen and other remotely located transducers (for example, transducers fixed at remote positions from the stylus) receive signals emanating from the mounted transducer as the stylus moves, making it possible (via triangulation, for example) to determine the position of the pen and ultimately to reproduce information associated with stylus movement. The position of the cylindrical film should be slightly higher than the tip of the pen because the height of the cylinder is typically 3–5 millimeters (mm) for a 80 KHz design and doubles for a 40 KHz design. The ultrasonic wave radiates from the center of the cylinder and the center of radiation is several millimeters above the pen tip. When the position of the pen tip is fixed on a point of the writing surface and the angle of pen is varied, the effective position of the cylindrical transducer moves, and false information is transmitted because the system is designed to detect the absolute position of the transducer. Therefore, during writing or using of the pen, a person has to hold the pen at an exact, constant angle in order for the system to work as designed with maximum accuracy. Moreover, such transducers have been typically mounted externally on the pen, which causes additional problems for both the user, who must hold the stylus, and for the signal detection/transmission circuitry. Structures disposed about the outer surface of the stylus in a ring-like manner and placement of the structure at or substantially near the location of the stylus tip interfere with the user's ability to adequately grasp or hold the stylus. In addition, such location operates as an obstruction to the user's viewing of the information as it is being written. Accordingly, a need exists to provide an improved transducer apparatus mountable within a stylus for transmitting acoustic signals.
It is to be understood that these drawings are solely for purposes of illustrating the concepts of the invention and are not intended as a level of the limits of the invention. It will be appreciated that the same reference numerals, possibly supplemented with reference characters where appropriate, have been used throughout to identify corresponding parts.